Background The implementation of advance care planning (ACP) in heart failure management is insufficient. Social isolation (SI) could be a barrier to ACP initiation, albeit the relationship between SI and patients' preference for ACP or end‐of‐life care remains unknown. Methods and Results We conducted a questionnaire survey, including assessments of SI using the 6‐item Lubben Social Network Scale as well as patients' perspectives on ACP and end‐of‐life care. Of the 160 patients approached by our multidisciplinary heart failure team during admission, 120 patients (75.0%) completed the survey (median age, 73.0 years; men, 74.2%). A Cox proportional hazard model was constructed to elucidate the short‐term (180‐day) prognostic impact of SI. Overall, 28.3% of participants were at high risk for SI (6‐item Lubben Social Network Scale score <12). High‐risk patients had more negative attitudes toward ACP than those without (61.8% versus 80.2%; P =0.035). The actual performance of ACP conversation in patients with and without high risk were 20.6% and 30.2%, respectively. Regarding preference in end‐of‐life care, “Saying what one wants to tell loved ones” (73.5% versus 90.6%; P =0.016) and “Spending enough time with family” (58.8% versus 77.9%; P =0.035) were less important in high‐risk patients. High risk for SI was associated with higher 180‐day risk‐adjusted all‐cause mortality (hazard ratio, 7.89 [95% CI, 1.53–40.75]). Conclusions In hospitalized patients with heart failure, high risk for SI was frequently observed. High‐risk patients were associated with a negative attitude toward ACP, despite higher mortality. Further research is required to establish an ideal approach to provide ACP in socially vulnerable patients.